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Thread: HEADSPACE QUESTIONS

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    HEADSPACE QUESTIONS

    My apologies if all of this has been covered before, but I don't recollect another thread that dealt with the subject comprehensively...

    Who should be concerned about headspace?
    I imagine that a shooter that buys a complete carbine and never shoots it enough to have to replace a bolt has little need to worry about headspace. What scenarios, however, necessitate verification of safe headspace with appropriate gauges? Replacing a broken bolt? Assembling an upper from parts chosen à la carte? Reaming a SAAMI-spec chamber to NATO spec? Swapping bolts between uppers?

    How often does headspace need to be checked?
    Is there a recommended interval at which headspace should be checked (e.g., every X-thousand rounds)?

    How does one verify proper headspace?
    I assume that headspace gauges are the only way to properly check headspace. Does one need a “Go” Gauge to check minimum headspace AND a “No-Go” Gauge to check maximum headspace? What is a “Field” Gauge, and how is it different than a “No-Go” Gauge? Does one need “military” gauges to check 5.56x45mm NATO and “civilian” gauges to check .223 Remington? What are the preferred brands of gauges?

    What is a “fitted” bolt?
    I see some vendors advertising “fitted” bolts sold along with a barrel. Does this mean that over-sized parts have actually been fitted for optimal headspace? Or does this simply mean that headspace has been gauged and verified to be safe?
    Aubrey<><

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    Quote Originally Posted by Aubrey View Post
    Who should be concerned about headspace?
    Everyone.
    We hope that all new guns are within spec, but it never hurts to verify it yourself.
    The following scenarios certainly necessitate verification of safe headspace with appropriate gauges:
    Replacing a broken bolt
    Assembling an upper from parts chosen à la carte
    Swapping bolts between uppers
    Reaming a SAAMI-spec chamber to NATO spec (this activity has the most risk of making excessive headspace)

    How often does headspace need to be checked?
    Is there a recommended interval at which headspace should be checked (e.g., every X-thousand rounds)?
    Once a year on any gun being fired at least 1000 rounds a year.
    On a heavier firing schedule, I think that every 3000 rounds is a good suggestion.

    How does one verify proper headspace?
    I assume that headspace gauges are the only way to properly check headspace. Does one need a “Go” Gauge to check minimum headspace AND a “No-Go” Gauge to check maximum headspace? What is a “Field” Gauge, and how is it different than a “No-Go” Gauge? Does one need “military” gauges to check 5.56x45mm NATO and “civilian” gauges to check .223 Remington? What are the preferred brands of gauges?
    "Go" is the minimum length that will let a chamber reliably accept ammunition that's within spec.
    "No-Go" is the maximum dimension for a NEW barrel and bolt pair.
    "Go" and "No-Go" gauges mostly reserved for people chambering barrels.
    If you don't have a reamer, you probably don't need these gauges.

    We are mostly concerned with the MAXIMUM dimension caused by use.
    "Field Service" gauges (known simply as field) determine if a specific bolt and barrel are still within acceptable standards.
    The suggested gauge is the Military field gauge.
    The easiest gauge to obtain is this one available at Brownells.
    Everyone with an AR-15 should own that one.

    In use, you knock out the ejector retainer pin, remove the ejector, snap the gauge under the extractor and insert it into the chamber with your bolt carrier group.
    The bolt should NOT close on this gauge.
    There will usually be a 3/16" to 1/4" gap at the front of the carrier which will be visible through the ejection port.
    IF the bolt and barrel accept this gauge, replace the bolt.
    If the new bolt also accepts the gauge, replace the barrel.

    Full details on gauge dimensions are available in my headspace info collection.

    It's interesting to note when comparing 223 to 5.56 that BOTH can be chambered to almost the same MINIMUM spec and still be well within spec.
    There's a LOT of bad info floating around about this.
    Everyone assumes that 5.56 chambers are automatically longer than 223 chambers.
    It's just not true.
    Read the headspace gauge specs I posted a link to and decide for yourself.
    Only the MAXIMUM lengths are longer, not the MINIMUM lengths.
    This is a very important distinction.
    The wider RANGE of acceptable headspace lengths allow for easier interchangability of parts from many different makers to all work reliably.

    My 223 and 5.56 reamer dimensions collection shows the true differences between all the DIAMETERS of the different reamers.
    This is where the major difference is.

    What is a “fitted” bolt?
    I see some vendors advertising “fitted” bolts sold along with a barrel. Does this mean that over-sized parts have actually been fitted for optimal headspace? Or does this simply mean that headspace has been gauged and verified to be safe?
    Depending on who you get the barrel from, it can have two meanings.
    By-far, the most common meaning is that the barrel and bolt have been checked for headspace.
    In a custom-made barrel situation, it's also possible to drastically reduce the "endspace" (my term for gap at the bolt lugs).
    This is more critical where you are searching for ultimate accuracy.
    By reducing the endspace, you force the bolt to stop against the barrel, not against the cartridge.
    This reduces the sizing that occurs within the chamber when the bolt is camming shut against the cartridge head.
    By elimininating this variable, the firing pin hit is more consistent and ignition can be more consistent, promoting the best accuracy obtainable.
    Endspace fitting can ONLY be done when you are making a barrel from scratch as it requires the actual bolt to live with the barrel during chambering and extension fitting.
    This is never done in a "production/factory" environment.

    Here's a picture showing how the bolt/barrel/barrel extension/cartridge interact.
    The "endspace" that I speak of is the gap between the front of the bolt lugs (red) and the rear of the barrel(blue).

    Randall Rausch
    AR15 Barrel Guru
    California Precision Rifle Club founding member

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    I would say, anytime you're going to be pairing up a bolt and barrel that haven't been used together would be a good time to check headspace.

    I've never seen an interval for checking it as far as round count, but anytime a weapon leaves my cage to be fired, I run all my gages through it. If it isn't going to be fired, I'm only required to do it annually. For personal use, I would only check initially and then maybe again if your groups start to open up after a while.

    I've only used a max headspace gage on the M16's, I guess I'd call it a No-Go guage. I would also guess that if your bolt closes on a round in the chamber, then you just passed the min headspace. I'm not sure if there is a difference in the 5.56mm and .223 headspace. I would think they seat at the same or close to the same depth.

    ETA: Woa, I guess I shoulda just waited a few mintues.

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    Quote Originally Posted by AR15barrels View Post
    Everyone.
    We hope that all new guns are within spec, but it never hurts to verify it yourself.
    The following scenarios certainly necessitate verification of safe headspace with appropriate gauges:
    Replacing a broken bolt
    Assembling an upper from parts chosen à la carte
    Swapping bolts between uppers
    Reaming a SAAMI-spec chamber to NATO spec (this one has the most risk of making excessive headspace)



    Once a year on any gun being fired at least 1000 rounds a year.
    On a heavier firing schedule, I think that every 3000 rounds is a good suggestion.
    In your experience, how much headspace growth occurs during these checks per thousand rounds? Any? Have you ever measured a bolt/barrel combo that was within spec when new, but grew to "Field Reject" dimensions by end of life? If so, how many rounds did it take?



    "Full details on gauge dimensions are available in my headspace info collection.

    It's interesting to note when comparing 223 to 5.56 that BOTH can be chambered to almost the same MINIMUM spec and still be well within spec.
    There's a LOT of bad info floating around the errornet about this.
    Everyone assumes that 5.56 chambers are longer than 223 chambers.
    Read the headspace gauge specs I posted a link to and decide for yourself.
    Absolutely. The real difference is in throat diameter dimension (and maybe leade, can't remember but I'm too lazy to look at your link) and headspace gauges don't measure those. Usage of a neck reamer can open up the throat/leade area but not lengthen any headspace.

    Does anyone make a throat erosion "pin" gauge that you can use to determine if the throat is 5.56 NATO diameter? How about leade, do erosion gauges measure freebore reliably?

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    Quote Originally Posted by jmart View Post
    In your experience, how much headspace growth occurs during tehse checks per thousand rounds? Any? Have you ever measured a bolt/barrel combo thatw as within spec when new, but grew to "Field Reject" dimensions by end of life? If so, how many rounds did it take?

    Does anyone make a throat erosion "pin" gauge that you can use to determine if the throat is 5.56 NATO diameter? How about leade, do erosion gauges measure freebore reliably?
    I don't get to see a gun throughout it's life and see logs that show how many rounds have caused how much wear.

    From my limited experience, I see a couple Tenths (of a thousandth) wear over a couple thousand rounds.
    It's not uncommon for a bolt to live MUCH longer than it's recommended service life before it develops excessive headspace.
    I have a Colt bolt in my 3gun rifle that has outlived two barrels.

    All you would need is a 0.226" gauge pin to check for a Nato leade dimension.
    Randall Rausch
    AR15 Barrel Guru
    California Precision Rifle Club founding member

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    Quote Originally Posted by jmart View Post
    The real difference is in throat diameter dimension (and maybe leade, can't remember but I'm too lazy to look at your link)
    Don't be lazy.
    Each of the two links I provided are single page PDF files.
    Very easy to understand.
    They even have pictures in them.
    You might actually learn something.

    The reamers comparison shows the diameters.

    5.56 throats are 0.2265"
    Most others are 0.224" to match the bullet diameter.
    Randall Rausch
    AR15 Barrel Guru
    California Precision Rifle Club founding member

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    Quote Originally Posted by AR15barrels View Post
    Don't be lazy.
    Each of the two links I provided are single page PDF files.
    Very easy to understand.
    They even have pictures in them.
    You might actually learn something.

    The reamers comparison shows the diameters.

    5.56 throats are 0.2265"
    Most others are 0.224" to match the bullet diameter.

    I have reviewed that page, many times. My recollection was that freebore/throat diameters were one of the main differences between NATO and SAAMI chambers, I just hadn't committed to memory the other deltas.

    That's great info that should be stickied. It really demonstrates what the differences are and you can see how a Wylde chamber compares to NATO and a SAAMI chamber, and how little difference there is in body dimensions. It's almost all in the freebore/leade area.

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    Quote Originally Posted by jmart View Post
    That's great info that should be stickied. It really demonstrates what the differences are and you can see how a Wylde chamber compares to NATO and a SAAMI chamber, and how little difference there is in body dimensions. It's almost all in the freebore/leade area.
    I'm glad you understand the differences.
    I just wish everyone else did too.
    It would help everyone's greater understanding of the rifles we have.
    Randall Rausch
    AR15 Barrel Guru
    California Precision Rifle Club founding member

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    Randall the gauge at Brownells says .223 is this ok for a 5.56 spec gun?
    Also im a techinical IDIOT and mechanical SCHMUCK! Is using this gauge easy for someone of my LOW sklill level? Its amazing what kind of idiot they will give a Doctorate to these days!

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    Quote Originally Posted by Shihan View Post
    Randall the gauge at Brownells says .223 is this ok for a 5.56 spec gun?
    Also im a techinical IDIOT and mechanical SCHMUCK! Is using this gauge easy for someone of my LOW sklill level? Its amazing what kind of idiot they will give a Doctorate to these days!
    Don't worry if it says 223 or 5.56 on the gauge.
    Worry about the actual DIMENSION of the gauge.

    This is covered in my headspace gauges info PDF file linked above.
    You did read that right...
    Randall Rausch
    AR15 Barrel Guru
    California Precision Rifle Club founding member

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